One way of displaying an analog wave representing a physiological function on a cathode ray tube in which the electron beam successively scans a series of parallel lines is to generate a ramp voltage that is proportional to the position of the electron beam as it scans each line and compare it with the analog wave. At the point of coincidence, the electron beam is intensity modulated so as to produce a bright dot. Thus, the analog wave is sampled once during the scanning of each line so as to build up an image formed from a series of dots.
In the portion of the analog wave having little slope, the dots are nearly touching so as to form a seemingly continuous line, but in portions of the analog wave having large slope, the dots are spread apart along the scanned lines so as to form a weak discontinuous line.
In order to overcome this problem, circuits have been provided that stretch the dots into line segments that fill in the spaces between the dots. Unfortunately, these circuits are complex and expensive.